Pressure transmitting fluids for brakes and hydraulic apparatus



PRESSURE TRANSMITTING FLUIDS FQR BRAKES AND HYDRAULIC APPARATUS Hilda Friedrich, Gendorf, Kurt Fischer, Altoetting, and Gunter Rummert, Burghausen, Salzach, Germany, assignors of one-half to Farbwerke Hoechst Aktie-ngeselischaft vormals Meister Lucius & Bruning, Frankfurt am Main, Germany, a corporation of Germany, and of one-half to'Alfred 'leves Maschineu-und Armature!!- fabrik Kommandit-Gasselschaft, Frankfurt am Main,

. Germany, a limited partnership, as tenants in common Application December -1, 1953 Serial No. 395,590

N Drawing.

Claims.

Pressure transmitting fluids for brakes and hydraulic apparatus are characterized, among other things, by good anti-freezing qualities and high lubricating power. Insofar as such hydraulic fluids have appeared on the market "in the past, they consisted, to a great extent, of castor ities but lack adequate lubricating power. Attempts have been made to increase the lubricating power by making mixtures, such as by adding castor oil to the aforementioned materials. However, it was not possible to maintain the anti-freezing qualities at the desired level when this was done. The problem is, therefore, to find addi tives, for hydraulic fluids having a polyglycol or polyglycol-ether base, which will increase the lubricating power but not affect the anti-freezing qualities,

Since, despite the disadvantage of having poor antifreezing qualities, castor oil-containing fluids are still very often used in industry, it is necessary that hydraulic fluids having a glycol base and containing castor oil be miscible with the castor oil in all proportions. It is therefore required that the additive for increasing lubricating power should not interfere with this miscibility. Under anhydrous conditions, polyglycolor glycol ethercontaining hydraulic fluids in suitable composition are miscible inall proportion with castor oil-containing fluids. Therefore, another condition is that the glycol-containing fluids be anhydrous.

It has now been established that hydraulic fluids which have good anti-freezing qualities and, furthermore, are compatible with castor oil-containing hydraulic fluids, are obtained if one adds, as a supplement to a liquid mixture having a base consisting essentially of anhydrous polyalcohols or ether-alcohols, certain quantities of phosphorous compounds, such as esters derived from the acids of phosphorous. Especially suitable as bases are diand triethylene glycol or other alkylene glycols, as well as ethyl, propyl and butyl polyglycols, used either individually or in mixtures; the bases may also be mixed with anhydrous solvents such as diacetone alcohol, lower alcohols and the like.

Additives which substantially increase the lubricating power are organic phosphorous compounds containing oxygen or sulphur, such as esters of phosphoric acid, thiophosphoric acid, phosphorous acid, phosphinous and phosphinic acid, phosphonous and phosphonic acid, as well as the esters of polyphosphorous acids. Especially simple to obtain and preferred because of their effective- States Patent 0 ness, are the neutral and acidic phosphoric acid esters of aliphatic polyoxyand polyhydroxy compounds, such as ethylene glycol, butylene glycol, glycerol and, particularly, polyethylene glycols. In the compounds meritionc'd, sulphur may replace oxygen. Very often the ef fect produced by individual components may be increased by using mixtures containing several of the above-described phosphorous compounds. In many cases, an increase in lubricating power may also be effected by a combination of phosphoric acid esters with boric acid esters or borates. In addition to the esters mentioned, oils, such as castor oil or other similar oils or derivatives thereof, may be added in such quantities that good antifreezing qualities are preserved.

The phosphorous-containing esters mentioned are added in amounts which may differ a great deal depending on the purpose for which the hydraulic fluids are to be used. v For ordinary requirements, in brake fluids which contain as a base, polyalcohols or their ethers and polyalkylene glycols (in admixture with other solvents if desired), an addition of 0.5 to 5.0% by weight is sufficient to increase the lubricating power of the base quite substantially.

Additives of the above described type increase the lubricating power considerably without affecting miscibility with castor oil-containing fluids. Moreover, they do not cause any undesirable changes in viscosity of the fluid at high or low temperatures; and the swelling capacity of the normally employed sealing materials (e.g. gaskets, washers, etc.) is practically uninfluenced by these additiv'es. To maintain the pH values necessary for satisfactory corrosion inhibition, the phosphoric acid esters are adjusted to pH 79 with ammonia, triethanol amine or other organic bases and to them are added the customary corrosion inhibitors, namely as inorganic or organic compounds giving a buflering effect, such as alkali salts of boric acid, benzoic acid, the phenyl glycines and mercaptobenzthiazol, etc.

Example 1 A hydraulic fluid consisting of:

43 parts by weight butyl polyglycol 6 parts by weight ethyl polyglycol 17 parts by weight diethylene glycol 34 parts by' weight triethylene glycol 0.3 parts by weight sodium mercaptoben'zthiazol and which shows very moderate lubricating power, can have its lubricating power improved considerably by adding 3 parts by weight pentaethyleneglycol secondary phosphate, adjusted to approximately pH 8.5 with triethanolamine in aqueoustest solution (1:9). The freezing point of this liquid is C.

The ethylpolyglycol, mentioned in the' above as well as the following examples, is essentially a mixture of diethylene and triethyleneglycol monoethylether in the proportion of about 2:1; the butyl polyglycol, mentioned in the above as well as the following examples, is essentially a mixture of diethylene and triethyleneglycol monobutylether in the proportion of about 2:1.

Example 2 A mixture of:

10 parts by weight ethyl glycol 70 parts by weight butyl polyglycol 19.5 parts by weight triethylene glycol 0.5 part by weight castor oil provided with the customary corrosion inhibitor is significantly improved in lubricating power by adding 0.5 part by weight pentaethyleneglycol tertiary phosphate and 0.5 part by weight pentaethyleneglycol secondary phosphate, both adjusted to about pH 8.5 (as in Example 1). The freezing point of the liquid is 70 C.

Example 3 A mixture of:

70 parts by weight butyl polyglycol and 30 parts by weight triethylene glycol including a minor quantity of corrosion inhibitor shows considerably increased lubricating power by adding to it 5 parts by weight of an alcoholysis product of castor oil with butyl diglycol and 0.5 part by weight pentaethyleneglycol tertiary phosphate adjusted with triethanolamine to about pH 8.5 (as in Example 1). The freezing point of the liquid is 70 C. and it is miscible with castol oil-containing hydraulic fluids.

Example 4 A mixture of:

30 parts by weight diethylene glycol and 70 parts by weight butyl polyglycol containing the customary corrosion inhibitor are significantly improved in lubricating power by adding 4 parts by weight triethyleneglycol tertiary phosphate, adjusted to pH 9 in aqueous test solution, and 3 parts by weight glycol triethanolamine borate. The freezing point is 75 C.

Example 5 A mixture of:

95 parts by weight ethyl polyglycol and 5 parts by weight triethylene glycol tertiary phosphate adjusted to pH 89.5 in aqueous test solution is provided with a minor quantity of corrosion inhibitor. This liquid has a freezing point of 70 C.

Example 6 55 parts by weight polyethylene glycol monobutyl ether parts by weight diethylene glycol 8 parts by weight triethylene glycol including a minor quantity of corrosion inhibitor is increased in lubricating power by adding 2 parts by weight of a mixed poly-condensed tertiary ester formed by esterification of 1 mol phosphoric acid and 1 mol boric acid with 3 mols of a mixture of tetra and pentaethylene glycol having an average molecular weight of 200. The

4 freezing point of this liquid is C. The liquid may be mixed with castor oil-containing hydraulic liquids.

The phosphoric acid-boric acid-mixed ester may be replaced by corresponding esters of other glycols and polyglycols.

What is claimed is:

1. A hydraulic fluid consisting essentially of a mixture of at least one alcohol selected from the group consisting of lower alkyl polyglycols, lower alkylene glycols and lower polyalkylene glycol ether bases together with a minor but lubricating increasing proportion up to 5% by weight of an ester which is the reaction product of an acid selected from the group consisting of phosphoric acid, thicphosphoric acid, phosphorous acid, phosphinous acid, phosphinic acid, phosphonous acid, phosphonic acid and polyphosphorous acids, and an alcohol selected from the group consisting of ethylene glycol, butylene glycol, glycerol and polyethylene glycols.

2. The hydraulic fluid of claim 1 which also contains diacetone alcohol as a solvent.

3. The hydraulic fluid of claim 1 which also contains triethanolamine as a pH adjuster.

4. A hydraulic fluid consisting essentially of a mixture of at least one alcohol selected from the group consisting of lower alkyl polyglycols, lower alkylene glycols and lower polyalkylene glycol ether bases together with a minor but lubricating increasing proportion up to 5% by weight of an ester which is the reaction product of an acid selected from the group consisting of phosphoric acid, thiophosphoric acid, phosphorous acid, phosphinous acid, phosphinic acid, phosphonous acid, phosphonic acid and polyphosphorous acids, and an alcohol selected from the group consisting of ethylene glycol, butylene glycol, glycerol and polyethylene glycols adjusted to a pH within the range 7-9 by the addition of a compound selected from the group consisting of the alkali salts of boric proportion by weight of a corrosion inhibitor selected acid, benzoic acid, the phenyl glycines and mercaptobenzthiazol.

5. A hydraulic fluid consisting essentially of polyethylene glycol monobutyl ether, a polyethylene glycol, and a minor but lubricating-increasing proportion up to 5% of a mixed poly-condensed tertiary ester formed by esterifying a mixture containing 1 mol of phosphoric acid and 1 mol of boric acid with 3 mols of a mixture of tetra and pentaethylene glycol.

References Cited in the file of this patent UNITED STATES PATENTS 2,169,231 Fife Aug. 15, 1939 2,462,694 Walker Feb. 22, 1949 2,469,285 White May 3, 1949 2,507,401 Doelling May 9, 1950 2,632,767 Smith et a1 Mar. 24, 1953 2,659,699 George et a1 Nov. 17, 1953 2,661,366 Gamrath et al. Dec. 1, 1953 2,665,312 Ohlmann et al. Jan. 5, 1954 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,916,457 December 8, 1959 Hilda Friedrich et a1 It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, lines 36 to 39, should appear as shown below instead of as in the patent:

from the group consisting of ammonia and Hiethanol amine together with a minor but corrosion-inhibiting proportion by weight of a corrosion inhibitor selected from the group consisting of the alkali salts of boric acid,

benzoic acid, the phenyl glycines and mercaptobenzthiazol.

Signed and sealed this 27th day of September 1960,

(SEAL) Attest:

KARL H. AXLINE ROBERT C; WATSON Attesting Officer Commissioner of Patents 

1. A HYDRAULIC FLUID CONSISTING ESSENTIALLY OF A MIXTURE OF AT LEAST ONE ALCOHOL SELECTED FROM THE GROUP CONSISTING OF LOWER ALKYL POLYGLYCOLS, LOWER ALKYLENE GLYCOLS AND LOWER POLYALKYLENE GLYCOL ETHER BASES TOGETHER WITH A MINOR BUT LUBRICATING INCREASING PROPORTION UP TO 5% BY WEIGHT OF AN ESTER WHICH IS THE REACTION PRODUCT OF AN ACID SELECTED FROM THE GROUP CONSISTING OF PHOSPHORIC ACID, THIOPHOSPHORIC ACID, PHOSPHOROUS ACID, PHOSPHINOUS ACID, PHOSPHINIC ACID, PHOSPHONOUS ACID, PHOSPHONIC ACID AND POLYPHOSPHOROUS ACIDS, AND AN ALCOHOL SELECTED FROM THE GROUP CONSISTING OF ETHYLENE GLYCOL, BUTYLENE GLYCOL, GLYCEROL AND POLYETHYLENE GLYCOLS. 